Healing and/or structural correction is greatly facilitated when a bone is fixed, i.e. stabilized, in the proper position. Various devices and techniques for stabilization of bone are well known and routinely practiced in the medical arts. Long bones have been stabilized using such devices as plates, slings, external casts, splints, screws and braces. The spine has been stabilized using rod and fastener systems. For example, fasteners such as screws, clamps, hooks, claws or bolts are placed into each vertebra and connected by a rod attached to the fasteners. Tension or compression force is applied to the rod between each consecutive fastener for fixation of the vertebrae. Such a system can be used on a single vertebra and/or on multiple vertebrae.
Bone screws are commonly used as fasteners for alignment and fixation of vertebral bodies. These screws are inserted into the spinal pedicle, the bony process projecting backward from the vertebral body, and stabilized with connecting rods placed longitudinally with regard to the vertebrae. Although surgical insertion of pedicle screws has successfully treated non-unions, instability, injuries and disease of the spine, it is not without disadvantages.
A serious post-operative complication after insertion of pedicle screws is impingement of the movement of facet joints. Facet joints link the vertebrae together and their hinge-like movement enables flexion (bending forward) and extension (bending backward) of the spine. When pedicle screws are connected the connecting elements are placed within an area that is normally an empty space. This infringement of space limits the range of motion of the facet joints. Additionally, if the pedicle screws are inserted percutaneously using a minimally invasive device, the tip which facilitates the insertion, but performs no other function, remains attached to the connecting rod further impinging space. A patient with impinged facet joints can suffer difficult and limited movement along with extreme discomfort and pain. The primary purpose of the surgical placement of pedicle screws is to improve and/or correct symptoms of back problems, thus these side effects are unacceptable.
Accordingly, a need exists in the surgical arts for connecting elements that are compatible with minimally invasive techniques and capable of providing effective stabilization, but are less bulky and less disruptive of normal vertebral functioning than the currently available connecting elements.